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OKIsItJustMe Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:05 AM
Original message
Effortless sailing with fluid flow cloak
http://www.eurekalert.org/pub_releases/2011-08/du-esw08...
Public release date: 11-Aug-2011

Contact: Richard Merritt
richard.merritt@duke.edu
919-660-8414
Duke University

Effortless sailing with fluid flow cloak

DURHAM, N.C. Duke engineers have already shown that they can "cloak" light and sound, making objects invisible -- now, they have demonstrated the theoretical ability to significantly increase the efficiency of ships by tricking the surrounding water into staying still.

"Ships expend a great deal of energy pushing the water around them out of the way as they move forward," said Yaroslav Urzhumov, assistant research professor in electrical and computer engineering at Duke's Pratt School of Engineering. "What our cloak accomplishes is that it reduces the mass of fluid that has to be displaced to a bare minimum.

"We accomplish this by tricking the water into being perfectly still everywhere outside the cloak," Urzhumov said. "Since the water is still, there is no shear force, and you don't have to drag anything extra with your object. So, comparing a regular vessel and a cloak of the same size, the latter needs to push a much smaller volume of water, and that's where the hypothesized energy efficiency comes from."

The results of Urzhumov's analysis were published online in the journal Physical Review Letters. The research was supported by the U.S. Office of Naval Research and a Multidisciplinary University Research Initiative (MURI) grant through the U.S. Army Research Office. Urzhumov works in the laboratory of David R. Smith, William Bevan Professor of electrical and computer engineering at Duke.


http://dx.doi.org/10.1103/PhysRevLett.107.074501
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GreenPartyVoter Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:11 AM
Response to Original message
1. Wicked cool!
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crim son Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:17 AM
Response to Original message
2. WOW!
First the worm that makes wholly new particles and now this. Happy Saturday!
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phantom power Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:45 AM
Response to Original message
3. is this one of those fluid analogs of negative-refractive-index tricks?
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OKIsItJustMe Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:47 AM
Response to Reply #3
5. So it would seem
Frankly, it seems like Science Fiction to me.
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mopinko Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:47 AM
Response to Original message
4. sounds a little perpetual energy machine to me.
but maybe i am just not smart enough to get it.
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OKIsItJustMe Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:53 AM
Response to Reply #4
6. Is this a little easier to accept?
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett...

Leave no trace

Fluid Flow Control with Transformation Media

Yaroslav A. Urzhumov and David R. Smith

Phys. Rev. Lett. 107, 074501 (Published August 11, 2011)

Fluid Dynamics

What do you get the wizard who already has an invisibility cloak? How about a wake-less swimsuit? New theoretical calculations published in Physical Review Letters show how a special porous material draped over an object can disguise its movements through water. By directing fluid smoothly around the object, this technology could reduce the viscous drag on ships and other vessels as they plow through the water.

In 2006, David Smith and Yaroslav Urzhumov at Duke University, North Carolina, were able to make a cylindrical object appear invisible to microwaves by guiding the light waves around the object. The cloak in their experiment was made of artificial metamaterials, whose light-response properties can be controlled by altering their physical shape. In this case, light entering the metamaterial device was bent in such a way that it emerged as if nothing were in its path. Similar sorts of materials have been constructed to hide objects from sound waves and water waves.

Now, Smith and Urzhumov have expanded the realm of invisibility to fluid flow. In their analytical model, they imagined a sphere sitting in a uniform flow and wrapped in a shell of porous material. In order to make the downstream wake disappear, the researchers varied the fluid resistance (or permeability) of the shell. Their computations showed that the shells permeability must be negative in certain regions, which implies fluid acceleration rather than deceleration. In principle, micropumps embedded throughout the porous material could perform the needed acceleration. If such a wake-reducing device could be made, the authors believe it would make ship transportation more fuel-efficient. Michael Schirber
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mopinko Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 10:59 AM
Response to Reply #6
7. it just seems a little hyperbolic.
they seem to throw out the micro pump thing as tho, well, they are micro, they don't use energy.
i am sure the net effect would be energy saving. just wish there was some sort of % stated here.
does sound very cool, tho.
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OKIsItJustMe Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 11:12 AM
Response to Reply #7
9. Fluid Flow Control with Transformation Media

Fluid Flow Control with Transformation Media

Yaroslav A. Urzhumov* and David R. Smith

Center for Metamaterials and Integrated Plasmonics, Pratt School of Engineering, Duke University, Durham, North Carolina 27708, USA (Received 11 June 2011; published 11 August 2011)
We introduce a new concept for the manipulation of fluid flow around three-dimensional bodies. Inspired by transformation optics, the concept is based on a mathematical idea of coordinate transformations and physically implemented with anisotropic porous media permeable to the flow of fluids. In two situationsfor an impermeable object placed either in a free-flowing fluid or in a fluid-filled porous mediumwe show that the object can be coated with an inhomogeneous, anisotropic permeable medium, such as to preserve the flow that would have existed in the absence of the object. The proposed fluid flow cloak eliminates downstream wake and compensates viscous drag, hinting at the possibility of novel propulsion techniques.

DOI: 10.1103/PhysRevLett.107.074501 | PACS numbers: 47.56.+r, 47.15.G␣, 47.85.L␣, 81.05.Rm



The medium with a negative permeability is an active medium: it must use external energy to provide acceleration rather than deceleration to the fluid permeating through the porous medium. A physical implementation of such a medium can be foreseen as a distribution of minute pumps that help propel the fluid and compensate in a controlled fashion the viscous pressure drop that exists due to the velocity gradient in the a < r < b region. Potential candidate technologies for such a directional acceleration on the micro-scale level are electro-osmotic, pneumatic, and piezoelectric micropumps.



They do have equations, but I cannot give you a meaningful excerpt within posting constraints.
Pierre de Fermat
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mopinko Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 11:14 AM
Response to Reply #9
10. geek jokes. gotta love 'em.
ok, pierre. you win.
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OKIsItJustMe Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 11:16 AM
Response to Reply #10
11. Our tree cutting friend has found a copy of the paper available for free
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lumberjack_jeff Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Aug-12-11 11:11 AM
Response to Original message
8. The full paper is available for free here
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